1. Field of the Inventions
The present inventions are related to image forming devices and valves that may, for example, be used in image forming devices.
2. Description of the Related Art
A wide variety of image forming devices are currently available. Such devices include, but are not limited to, printers, plotters, facsimile machines, copiers, and “all-in-one” devices that are capable of printing, copying, scanning and facsimile transmission. Ink-jet pens (“or print cartridges”) are provided in many image forming devices. Such pens typically include a printhead with an orifice plate that has a plurality of small nozzles. Ink is ejected through the nozzles to form images by, for example, heating the ink with heating elements that are associated with respective nozzles. The nozzles are connected to a passive regulator, which maintains the internal pen pressure, by an internal valve and capillary tubes. Ink reservoirs, which may be positioned at remote locations within or near the image forming devices, are used to supply ink to the ink-jet pens by way of a supply line. Many ink reservoirs are pressurized so that they will be able to deliver ink to the pens regardless of the position of the reservoirs relative to the pens.
In order to prevent leakage, the pressure at the printhead in some image forming devices will be slightly lower than the ambient atmospheric pressure (referred to herein as “back-pressure”) when the pen is powered off and the ink pressure source is removed. The back-pressure must be large enough to prevent leakage when the pens are not in use, and small enough to allow the printhead, when activated, to overcome the back-pressure and eject ink droplets in a consistent and predictable manner. Too much back-pressure can cause ink back flow which may, in turn, siphon enough ink out of the pen nozzles and capillary tubes to dry out the nozzles and capillary tubes, thereby “de-priming” the pen. De-priming the capillary tubes reduces the nozzle suction to a level that is insufficient to pull ink into the nozzle. This can cause the printheads to overheat and fail, and most pens are incapable of self-priming to restart the ink flow after being de-primed. Additionally, as a pen is de-primed, excess air will be drawn into the regulator and cause the regulator to malfunction.
The present inventors have determined that the back-pressure within ink supply lines can occasionally be too high for the pressure regulators which, in turn, will result in de-priming and damage to the printheads. The present inventors have also determined that the passive pressure regulators associated with the pens are not designed to maintain a seal for long periods of time and, accordingly, can leak. If the pressure regulators leak, de-priming may occur even in those instances where the back-pressure is not too high for the pressure regulators.